NORD USS and Modbus RTU Manual
68 Subject to technical amendments BU 0050 GB-3111
2.6 Exception Responses
If a query by the Modbus Master cannot be answered correctly, an error message is sent instead of the normal
response. The error message is structured as follows:
0x80 + Function code of the Master query
A function code has been sent, which is not supported by the FI.
The telegram which has been sent is too long.
For read queries, the data range to be read out is too large.
The queried parameter is not known.
The parameter sub-index is not known.
An incorrect data content has been transmitted in the function "Write Single Coil".
The number of parameters is above the limit set by Modbus.
Error in access to the parameter database of the FI.
The number of coils to be written in the function "Write Single Coil" has been
exceeded
The Slave is still occupied with current query and cannot receive a new order.
Example:
Parameter P102, parameter set 2 is written with the value 0x0123.
Response (Slave Master)
2.7 Watchdog
Modbus communication can be monitored via the parameter P513. Monitoring is started with the first valid
telegram. If the FI does not receive a new telegram within the time set in P513, error 10.0 is triggered in the FI.
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